Chloroplasts contain a ferredoxin/thioredoxin system comprised of ferredoxin, ferredoxin-thioredoxin reductase and thioredoxins f and m that links light to the regulation of enzymes of photosynthesis (Buchanan, B. B. (1991) "Regulation of CO.sub.2 assimilation in oxygenic photosynthesis: The ferredoxin/thioredoxin system. Perspective on its discovery, present status and future development", Arch. Biochem. Biophys. 288:1-9; Scheibe, R. (1991), "Redox-modulation of chloroplast enzymes. A common principle for individual control", Plant Physiol. 96: 1-3). Several studies have shown that plants also contain a system, analogous to the one established for animals and most microorganisms, in which thioredoxin (h-type) is reduced by NADPH and the enzyme, NADP-thioredoxin reductase (NTR) according to the following: ##STR1##
(Florencio F. J., et al. (1988), Arch. Biochem. Biophys. 266: 496-507; Johnson, T. C., et al. (1987), Plant Physiol. 85: 446-451; Suske, G., et al. (1979), Z. Naturforsch. C. 34: 214-221). Current evidence suggests that the NADP/thioredoxin system is widely distributed in plant tissues and is housed in the mitochondria, endoplasmic reticulum and cytosol (Bodenstein-Lang, J., et al. (1989), FEBS Lett. 258: 22-26; Marcus, F., et al. (1991), Arch. Biochem. Biophys. 287: 195-198).
Thioredoxin h is also known to reductively activate cytosolic enzyme of carbohydrate metabolism, pyrophosphate fructose-6-P, 1-phosphotransferase or PFP (Kiss, F., et al. (1991), Arch. Biochem. Biophys. 287: 337-340).
The seed is the only tissue for which the NADP/thioredoxin system has been ascribed physiological activity in plants. Also, thioredoxin h has been shown to reduce thionins in the laboratory (Johnson, T. C., et al. (1987), Plant Physiol. 85: 446-451). Thionins are soluble cereal seed proteins, rich in cystine. In the Johnson, et al. investigation, wheat purothionin was experimentally reduced by NADPH via NADP-thioredoxin reductase (NTR) and thioredoxin h according to Eqs. 2 and 3. ##STR2##
Cereal seeds such as wheat, rye, barley, corn, millet, sorghum and rice contain four major seed protein groups. These four groups are the albumins, globulins, gliadins and the glutenins or corresponding proteins. The thionins belong to the albumin group or faction. Presently, wheat and rye are the only two cereals from which gluten or dough has been formed. Gluten is a tenacious elastic and rubbery protein complex that gives cohesiveness to dough. Gluten is composed mostly of the gliadin and glutenin proteins. It is formed when rye or wheat dough is washed with water. It is the gluten that gives bread dough its elastic type quality. Flour from other major crop cereals barley, corn, sorghum, oat, millet and rice and also from the plant, soybean do not yield a gluten-like network under the conditions used for wheat and rye.
Glutenins and gliadins are cystine containing seed storage proteins and are insoluble. Storage proteins are proteins in the seed which are broken down during germination and used by the germinating seedling to grow and develop. Prolamines are the storage proteins in grains other than wheat that correspond to gliadins while the glutelins are the storage proteins in grains other than wheat that correspond to glutenins. The wheat storage proteins account for up to 80% of the total seed protein (Kasarda, D. D., et al. (1976), Adv. Cer. Sci. Tech. 1: 158-236; and Osborne, T. B., et al. (1893), Amer. Chem. J. 15: 392-471). Glutenins and gliadins are considered important in the formation of dough and therefore the quality of bread. It has been shown from in vitro experiments that the solubility of seed storage proteins is increased on reduction (Shewry, P. R., et al. (1985), Adv. Cer. Sci. Tech. 7: 1-83). However, previously, reduction of glutenins and gliadins was thought to lower dough quality rather than to improve it (Dahle, L. K., et al. (1966), Cereal Chem. 43: 682-688). This is probably because the non-specific reduction with chemical reducing agents caused the weakening of the dough.
The "Straight Dough" and the "Pre-Ferment" methods are two major conventional methods for the manufacture of dough and subsequent yeast raised bread products.
For the Straight Dough method, all of the flour, water or other liquid, and other dough ingredients which may include, but are not limited to yeast, grains, salt, shortening, sugar, yeast nutrients, dough conditioners, and preservatives are blended to form a dough and are mixed to partial or full development. The resulting dough may be allowed to ferment for a period of time depending upon specific process or desired end-product characteristics.
The next step in the process is the mechanical or manual division of the dough into appropriate size pieces of sufficient weight to ensure achieving the targeted net weight after baking, cooling, and slicing. The dough pieces are often then rounded and allowed to rest (Intermediate Proof) for varying lengths of time. This allows the dough to "relax" prior to sheeting and molding preparations. The time generally ranges from 5-15 minutes, but may vary considerably depending on specific processing requirements and formulations. The dough pieces are then mechanically or manually formed into an appropriate shape are then usually given a final "proof" prior to baking. The dough pieces are then baked at various times, temperatures, and steam conditions in order to achieve the desired end product.
In the Pre-Ferment method, yeast is combined with other ingredients and allowed to ferment for varying lengths of time prior to final mixing of the bread or roll dough. Baker's terms for these systems include "Water Brew", "Liquid Ferment", "Liquid Sponge", and "Sponge/Dough". A percentage of flour ranging from 0-100% is combined with the other ingredients which may include but are not limited to water, yeast, yeast nutrients and dough conditioners and allowed to ferment under controlled or ambient conditions for a period of time. Typical times range from 1-5 hours. The ferment may then be used as is, or chilled and stored in bulk tanks or troughs for later use. The remaining ingredients are added (flour, characterizing ingredients, additional additives, additional water, etc.) and the dough is mixed to partial or full development.
The dough is then allowed to ferment for varying time periods. Typically, as some fermentation has taken place prior to the addition of the remaining ingredients, the time required is minimal (i.e., 10-20 min.), however, variations are seen depending upon equipment and product type. Following the second fermentation step, the dough is then treated as in the Straight Dough Method.
As used herein the term "dough mixture" describes a mixture that minimally comprises a flour or meal and a liquid, such as milk or water.
As used herein the term "dough" describes an elastic, pliable protein network mixture that minimally comprises a flour, or meal and a liquid, such as milk or water.
As used herein the term "dough ingredient" may include, but is not exclusive of, any of the following ingredients: flour, water or other liquid, grain, yeast, sponge, salt, shortening, sugar, yeast nutrients, dough conditioners and preservatives.
As used herein, the term "baked good" includes but is not exclusive of all bread types, including yeast-leavened and chemically-leavened and white and variety breads and rolls, english muffins, cakes and cookies, confectionery coatings, crackers, doughnuts and other sweet pastry goods, pie and pizza crusts, pretzels, pita and other flat breads, tortillas, pasta products, and refrigerated and frozen dough products.
While thioredoxin has been used to reduce albumins in flour, thiol redox proteins have not been used to reduce glutenins and gliadins nor other water insoluble storage proteins, nor to improve the quality of dough and baked goods. Thiol redox proteins have also not been used to improve the quality of gluten thereby enhancing its value nor to prepare dough from crop cereals such as barley, corn, sorghum, oat, millet and rice or from soybean flour.
Many cereal seeds also contain proteins that have been shown to act as inhibitors of enzymes from foreign sources. It has been suggested that these enzyme inhibitors may afford protection against certain deleterious organisms (Garcia-Olmedo, F., et al. (1987), Oxford Surveys of Plant Molecular and Cell Biology 4: 275-335; Birk, Y. (1976), Meth. Enzymol. 45: 695-739, and Laskowski, M., Jr., et al. (1980), Ann. Reo. Biochem. 49: 593-626). Two such type enzyme inhibitors are amylase inhibitors and trypsin inhibitors. Furthermore, there is evidence that a barley protein inhibitor (not tested in this study) inhibits an .alpha.-amylase from the same source (Weselake, R. J., et al. (1983), Plant Physiol. 72: 809-812). Unfortunately, the inhibitor protein often causes undesirable effects in certain food products. The trypsin inhibitors in soybeans, notably the Kunitz trypsin inhibitor (KTI) and Bowman-Birk trypsin inhibitor (BBTI) proteins, must first be inactivated before any soybean product can be ingested by humans or domestic animals. It is known that these two inhibitor proteins become ineffective as trypsin inhibitors when reduced chemically by sodium borohydride (Birk, Y. (1985), Int. J. Peptide Protein Res. 25: 113-131, and Birk, Y. (1976), Meth. Enzymol. 45: 695-739). These inhibitors like other proteins that inhibit proteases contain intramoelcular disulfides and are usually stable to inactivation by heat and proteolysis (Birk (1976), supra.; Garcia-Olmedo, et al. (1987), supra., and Ryan (1980). Currently, to minimize the adverse effects caused by the inhibitors these soybean trypsin inhibitors and other trypsin inhibitors in animal and human food products are being treated by exposing the food to high temperatures. The heat treatment, however, does not fully eliminate inhibitor activity. Further, this process is not only expensive but it also destroys many of the other proteins which have important nutritional value. For example, while 30 min at 120.degree. C. leads to complete inactivation of the BBTI of soy flour, about 20% of the original KTI activity remains (Friedman, et al., 1991). The prolonged or higher temperature treatments required for full inactivation of inhibitors results in destruction of amino acids such as cystine, arginine, and lysine (Chae, et al., 1984; Skrede and Krogdahl, 1985).
There are also several industrial processes which require .alpha.-amylase activity. One example is the malting of barley which requires active .alpha.-amylase. Inactivation of inhibitors such as the barley amylase/subtilisin (asi) inhibitor and its equivalent in other cereals by thiol redox protein reduction would enable .alpha.-amylases to become fully active sooner than with present procedures, thereby shortening time for malting or similar processes.
Thiol redox proteins have also not previously been used to inactivate trypsin or amylase inhibitor proteins. The reduction of trypsin inhibitors such as the Kunitz and Bowman-Birk inhibitor proteins decreases their inhibitory effects (Birk, Y. (1985), Int. J. Peptide Protein Res. 25: 113-131). A thiol redox protein linked reduction of the inhibitors in soybean products designed for consumption by humans and domestic animals would require no heat or lower heat than is presently required for protein denaturization, thereby cutting the costs of denaturation and improving the quality of the soy protein. Also a physiological reductant, a so-called clean additive (i.e., an additive free from ingredients viewed as "harmful chemicals") is highly desirable since the food industry is searching for alternatives to chemical additives. Further the ability to selectively reduce the major wheat and seed storage proteins which are important for flour quality (e.g., the gliadins and the glutenins) in a controlled manner by a physiological reductant such as a thiol redox protein would be useful in the baking industry for improving the characteristics of the doughs from wheat and rye and for creating doughs from other grain flours such as cereal flours or from cassava or soybean flour.
The family of 2S albumin proteins characteristic of oil-storing seeds such as castor bean and Brazil nut (Kreis, et al. 1989; Youle and Huang, 1981) which are housed within protein bodines in the seed endosperm or cotyledons (Ashton, et al. 1976; Weber, et al. 1980), typically consist of dissimilar subunits connected by two intermolecular disculfide bonds--one subunit of 7 to 9 kDa and the other of 3 to 4 kDa. The large subunit contians two intramolecular disculfide groups, the small subunit contains none. The intramolecular disculfides of the 2S large subunit show homology with those of the soybean Bowman-Birk inhibitor (Kreis, et al. 1989) but nothing is known of the ability of 2S proteins to undergo reduction under physiological conditions.
These 2S albumin proteins are rich in methionine. Recently transgenic soybeans which produce Brazil nut 2S protein have been generated. Reduction of the 2S protein in such soybeans could enhance the integration of the soy proteins into a dough network resulting in a soybread rich in methionine. In addition, these 2S proteins are often allergens. Reduction of the 2S protein would result in the cessation of its allergic activity.
Pullulanase ("debranching enzyme") is an enzyme that breaks down the starch of the endosperm of cereal seeds by hydrolytically cleaving .alpha.-1,6 bonds. Pullulanase is an enzyme fundamental to the brewing and baking industries. Pullulanase is required to break down starch in malting and in certain baking procedures carried out in the absence of added sugars or other carbohydrates. Obtaining adequate pullulanase activity is a problem especially in the malting industry. It has been known for some time that dithiothreitol (DTT, a chemical reductant for thioredoxin) activates pullulanase of cereal preparations (e.g., barley, oat and rice flours). A method for adequately activating or increasing the activity of pullulanase with a physologically acceptable system, could lead to more rapid malting methods and, owing to increased sugar availability, to alcoholic beverages such as beers with enhanced alcoholic content.
Death and permanent injury resulting from snake bites are serious problems in many African, Asian and South American countries and also a major concern in several southern and western areas of the United States. Venoms from snakes are characterized by active protein components (generally several) that contain disulfide (S--S) bridges located in intramolecular (intrachain) cystines and in some cases in intermolecular (interchain) cystines. The position of the cystine within a given toxin group is highly conserved. The importance of intramolecular S--S groups to toxicity is evident from reports showing that reduction of these groups leads to a loss of toxicity in mice (Yang, C. C. (1967) Biochim. Biophys. Acta. 133: 346-355; Howard, B. D., et al. (1977) Biochemistry 16: 122-125). The neurotoxins of snake venom are proteins that alter the release of neurotransmitter from motor nerve terminals and can be presynaptic or postsynaptic. Common symptoms observed in individuals suffering from snake venom neurotoxicity include swelling, edema and pain, fainting or dizziness, tingling or numbing of affected part, convulsions, muscle contractions, renal failure, in addition to long-term necrosis and general weakening of the individual, etc.
The presynaptic neurotoxins are classified into two groups. The first group, the .beta.-neurotoxins, include three different classes of proteins, each having a phospholipase A.sub.2 component that shows a high degree of conservation. The proteins responsible for the phospholipase A.sub.2 activity have from 6 to 7 disulfide bridges. Members of the .beta.-neurotoxin group are either single chain (e.g., caudotoxin, notexin and agkistrodotoxin) or multichain (e.g., crotoxin, ceruleotoxin and Vipera toxin). .beta.-bungarotoxin, which is made up of two subunits, constitutes a third group. One of these subunits is homologous to the Kunitz-type proteinase inhibitor from mammalian pancreas. The multichain .beta.-neurotoxins have their protein components linked ionically whereas the two subunits of .beta.-bungarotoxin are linked covalently by an intermolecular disulfide. The B chain subunit of .beta.-bungarotoxin, which is also homologous to the Kunitz-type proteinase inhibitor from mammalian pancreas, has 3 disulfide bonds.
The second presynaptic toxin group, the facilitatory neurotoxins, is devoid of enzymatic activity and has two subgroups. The first subgroup, the dendrotoxins, has a single polypeptide sequence of 57 to 60 amino acids that is homologous with Kunitz-type trypsin inhibitors from mammalian pancreas and blocks voltage sensitive potassium channels. The second subgroup, such as the fasciculins (e.g., fasciculin 1 and fasiculin 2) are cholinesterase inhibitors and have not been otherwise extensively studied.
The postsynaptic neurotoxins are classified either as long or short neurotoxins. Each type contains S--S groups, but the peptide is unique and does not resemble either phospholipase A.sub.2 or the Kunitz or Kunitz-type inhibitor protein. The short neurotoxins (e.g., erabutoxin a and erabutoxin b) are 60 to 62 amino acid residues long with 4 intramolecular disulfide bonds. The long neurotoxins (e.g., .alpha.-bungarotoxin and .alpha.-cobratoxin) contain from 65 to 74 residues and 5 intramolecular disulfide bonds. Another type of toxins, the cytotoxins, acts postsynaptically but its mode of toxicity is ill defined. These cytotoxins show obscure pharmacological effects, e.g., hemolysis, cytolysis and muscle depolarization. They are less toxic than the neurotoxins. The cytotoxins usually contain 60 amino acids and have 4 intramolecular disulfide bonds. The snake venom neurotoxins all have multiple intramolecular disulfide bonds.
The current snake antitoxins used to treat poisonous snake bites following first aid treatment in individuals primarily involve intravenous injection of antivenom prepared in horses. Although it is not known how long after envenomation the antivenom can be administered and be effective, its use is recommended up to 24 hours. Antivenom treatment is generally accompanied by administration of intravenous fluids such as plasma, albumin, platelets or specific clotting factors. In addition, supporting medicines are often given, for example, antibiotics, antihistamines, antitetanus agents, analgesics and sedatives. In some cases, general treatment measures are taken to minimize shock, renal failure and respitory failure. Other than administering calcium-EDTA in the vicinity of the bite and excising the wound area, there are no known means of localized treatment that result in toxin neutralization and prevention of toxic uptake into the blood stream. Even these localized treatments are of questionable significance and are usually reserved for individuals sensitive to horse serum (Russell, F. E. (1983) Snake Venom Poisoning, Schollum International, Inc. Great Neck, N.Y.).
The term "individual" as defined herein refers to an animal or a human.
Most of the antivenoms in current use are problematic in that they can produce harmful side effects in addition to allergic reactions in patients sensitive to horse serum (up to 5% of the patients). Nonallergic reactions include pyrogenic shock, and complement depletion (Chippaur, J.-P., et al. (1991) Reptile Venoms and Toxins, A. T. Tu, ed., Marcel Dekker, Inc., pp. 529-555).
It has been shown that thioredoxin, in the presence of NADPH and thioredoxin reductase reduces the bacterial neurotoxins tetanus and botulinum A in vitro (Schiavo, G., et al. (1990) Infection and Immunity 58: 4136-4141; Kistner, A., et al. (1992) Naunvn-Schmiedebera's Arch Pharmacol 345: 227-234). Thioredoxin was effective in reducing the interchain disulfide link of tetanus toxin and such reduced tetanus toxin was no longer neurotoxic (Schiavo, et al., supra.). However, reduction of the interchain disulfide of botulinum A toxin by thioredoxin was reported to be much more sluggish (Kistner, et al., supra.). In contrast to the snake neurotoxin studied in the course of this invention, the tetanus research group (Schiavo, et al., supra.) found no evidence in the work done with the tetanus toxin that reduced thioredoxin reduced toxin intrachain disulfide bonds. There was also no evidence that thioredoxin reduced intrachain disulfides in the work done with botulinum A. The tetanus and botulinum A toxins are significantly different proteins from the snake neurotoxins in that the latter (1) have a low molecular weight; (2) are rich in intramolecular disulfide bonds; (3) are resistant to trypsin and other animal proteases; (4) are active without enzymatic modification, e.g., proteolytic cleavage; (5) in many cases show homology to animal proteins, such as phospholipase A.sub.2 and Kunitz-type proteases; (6) in most cases lack intermolecular disulfide bonds, and (7) are stable to agents such as heat and proteases.
Reductive inactivation of snake toxins in vitro by incubation with 1% .beta.-mercaptoethanol for 6 hours and incubation with 8M urea plus 300 mM .beta.-mercaptoethanol has been reported in the literature (Howard, B. D., et al. (1977) Biochemistry 16: 122-125; Yang, C. C. (1967) Biochim. Biophys. Acta. 133: 346-355). These conditions, however, are far from physiological. As defined herein the term "inactivation" with respect to a toxin protein means that the toxin is no longer biologically active in vitro, in that the toxin is unable to link to a receptor. Also as used herein, "detoxification" is an extension of the term "inactivation" and means that the toxin has been neutralized in an individual as determined by animal toxicity tests.
Bee venom is a complex mixture with at least 40 individual components, that include major components as melittin and phospholipase A.sub.2, representing respectively 50% and 12% of the total weight of the venom, and minor components such as small proteins and peptides, enzymes, amines, and amino acids.
Melittin is a polypeptide consisting of 26 amino acids with a molecular weight of 2840. It does not contain a disulfide bridge. Owing to its high affinity for the lipid-water interphase, the protein permeates the phospholipid bilayer of the cell membranes, disturbing its organized structure. Melittin is not by itself a toxin but it alters the structure of membranes and thereby increases the hydrolitic activity of phospholipase A.sub.2, the other major component and the major allergen present in the venom.
Bee venom phospholipase A.sub.2 is a single polypeptide chain of 128 amino acids, is cross-linked by four disulfide bridges, and contains carbohydrate. The main toxic effect of the bee venom is due to the strong hydrolytic activity of phospholipase A.sub.2 achieved in association with melittin.
The other toxic proteins in bee venom have a low molecular weight and contain at least two disulfide bridges that seem to play an important structural role. Included are a protease inhibitor (63-65 amino acids), MCD or 401-peptide (22 amino acids) and apamin (18 amino acids).
Although there are thousands of species of bees, only the honey bee, Apis mellifera, is a significant cause of allergic reactions. The response ranges from local discomfort to systemic reactions such as shock, hypotension, dyspnea, loss of consciousness, wheezing and/or chest tightness that can result in death. The only treatment that is useed in these cases is the injection of epinephrine.
The treatment of bee stings is important not only for individuals with allergic reactions. The "killer" or Africanized bee, a variety of honey bee is much more agressive than European honey bees and represents a danger in both South and North America. While the lethality of the venom from the Africanized and European bees appears to be the same (Schumacher, M. I., et al. (1989) Nature 337: 413), the behaviour pattern of the hive is completely different. It was reported that Africanized bees respond to colony disturbance more quickly, in greater numbers and with more stinging (Collins, A. M., et al. (1982) Science 218: 72-74). A mass attack by Africanized bees may produce thousands of stings on one individual and cause death. The "killer" bees appeared as a result of the interbreeding between the African bee (Apis mellifera scutellata) and the European bee (Apis mellifera mellifera). African bees were introduced in 1956 into Brazil with the aim of improving honey production being a more tropically adapted bee. Africanized bees have moved from South America to North America, and they have been reported in Texas and Florida.
In some areas of the world such as Mexico, Brazil, North Africa and the Middle East, scorpions present a life hazard to humans. However, only the scorpions of family Buthidae (genera, Androctonus, Buthus, Centruroides, Leiurus and Tityus) are toxic for humans. The chemical composition of the scorpion venom is not as complex as snake or bee venom. Scorpion venom contains mucopolysaccharides, small amounts of hyaluronidase and phospholipase, low molecular-weight molecules, protease inhibitors, histamine releasers and neurotoxins, such as serotonin. The neurotoxins affect voltage-sensitive ionic channels in the neuromuscular junction. The neurotoxins are basic polypeptides with three to four disulflde bridges and can be classified in two groups: peptides with from 61 to 70 amino acids, that block sodium channel, and peptides with from 36 to 39 amino acids, that block potassium channel. The reduction of disulfide bridges on the neurotoxins by nonphysiological reductants such as DTT or .beta.-mercaptoethanol (Watt, D. D., et al. (1972) Toxicon 10: 173-181) lead to loss of their toxicity.
Symptoms of animals stung by poisonous scorpions inclure hyperexcitability, dyspnea, convulsions, paralysis and death. At present, antivenin is the only antidote for scorpion stings. The availability of the venom is a major problem in the production of antivenin. Unlike snake venom, scorpion venom is very difficult to collect, because the yield of venom per specimen is limited and in some cases the storage of dried venom leads to modification of its toxicity. An additional problem in the production of antivenins is that the neurotoxins are very poor antigens.
The reductive inactivation of snake, bee and scorpion toxins under physiological conditions has never been reported nor has it been suggested that the thiol redox agents, such as reduced lipoic acid, DTT, or reduced thioredoxin could act as an antidote to these venoms in an individual.